Electrical accessories are mainly constituted by an accessory support in the form of a frame for fitting on the open front face of an electrical box, an accessory mechanism (e.g. a switch or a power outlet) for blocking in the opening defined by the accessory support, and a cover plate for fastening on the accessory support so that it covers said accessory support, and so that it borders the accessory mechanism in attractive manner.
The accessory support may be fastened on the electrical box in various ways.
Typically, an electrical box includes two screw-fastener wells that project from its rear wall along the inside face of its side wall. At the center of each of its four branches, the accessory support includes a corresponding orifice in the shape of a key hole for passing a fastener screw engaged in one of the screw-fastener wells of the electrical box.
Since such screw-fastening is tricky to use, other fastener systems have been developed.
Thus, document U.S. Pat. No. 2,934,590 discloses a power outlet comprising an accessory support that is flanked by two spring blades that are bent into a U-shape, each spring blade presenting an end that is fastened to the support, and a free end that is adapted to be engaged in a slot formed in the side wall of the electrical box.
In that document, the cover plate includes two flexible tongues that are adapted to be engaged between the arms of the spring blades, and having ends that are bent so as to catch on the spring blades.
That system presents a major drawback, namely that the snap-fastening of the accessory support to the box may fail.
Thus, the installer may wrongly believe that the support is snap-fastened properly to the electrical box, even though one of the spring blades is not engaged in the corresponding slot of the box. Thus, there is a risk that the user, while attempting to unplug an electric plug from the power outlet, pulls out the power outlet.
In addition, even when the spring blades are engaged properly in the slots of the electrical box, a traction force exerted on the electric plug risks causing the spring blades to flex, which can also result in the power outlet being pulled out from the electrical box. The tongues of the cover plate are flexible and thus would not prevent the spring blades from flexing.
That system presents another drawback, namely that it does not make it possible in any way to adjust the spacing between the cover plate and the electrical box.
Unfortunately, after blocking the electrical box in the wall, it often happens that the wall is covered with a covering (wallpaper, plaster, . . . ) that generates extra thickness. Thus, the extra thickness prevents the installer from fastening the cover plate to the accessory support.
In addition, document DE 91 06 123 discloses an electrical accessory comprising an electrical box that is engaged in a wall panel, a power-outlet mechanism, and a cover plate.
In its side wall, the electrical box presents slots that are situated level with cavities that are formed in the wall panel.
The power-outlet mechanism includes two opposite snap-fastener tabs that carry firstly teeth that are adapted to snap-fasten in the slots of the electrical box and in the cavities of the wall panel, and secondly levers.
Finally, the cover plate presents a front wall in the form of a frame, and tongues that extend from the inner edge of the front wall, towards the rear, so as to block the levers in such a manner that the teeth of the snap-fastener tabs of the power-outlet mechanism cannot come out of the slots of the electrical box.
In that embodiment, the cover plate is fastened on the electrical box via the outer peripheral rim of the cover plate, which outer peripheral rim presents a groove that is set back and that is adapted to snap-fasten on a collar that borders the front of the electrical box.